Process of forming hollow articles from oriented polymer



April 13, 1948. R. w. CANFIELD El AL PROCESS OF FORMING HOLLOW ARTICLESFROM ORIENTED POLYMER Filed Jan. 27, 1944 3 Sheets-Sheet 1 171' Sheef 0Oriel 2+9; 28 26 Wlf H II " u Illlll IIIIII llll id m #9 w 0, 2 nn qc n9/0 r 66%? W w n i A 0 brf m 2 A3 4 b Orien fed Polymer Witness:

a. a M

Apnl 13, 1948. R. w. CANFIELD El AL ,7 6

PROCESS OF FORMING HOLLOW ARTICLES FROM ORIENTED POLYMER Filed Jan 27,1944 s Sheets-Sheet 2' In I Ki In ven tons:

I Rob erf 14/. Canf/e/d Non-L am e/Iar p E l/v yqy h r i 1 fed A nfoneM. Guerra/r0 Miness. Polymer big l A ttornqys.

April 13, 1948. R. w. CANFIELD ET AL 2, 6

PROCESS OF FORMING HOLLOW ARTICLES FROM ORIENTED POLYMER Filed Jan. 271944 3 Sheets-Sheet 3 EQIZ K 47a 1 5 112 can tors.-

4 fed I 54 'Roberf 14 Canf/e/a Polymer Fred il 1 4 (i-H1938. I ljlg0l7.Guerre/ro A I torn qys.

referred to are of the type Patented Apr. 13, 1948 'l/UNITED S TATE-SPATENT" OFFICE 21,439,716 PROCESS or FOR G HOLLOW ARTICLES FRoM ORIENTEDPOLYMER. l

Robert w. Oanfield and Fred E1. Wiley, West Hartford, and

Antone M. Guerreiro, Hartford,

Conn., assignors to Plax Corporation, Hartford, Conn, a corporation ofDelaware Application January 27, 1944, Serial No. 519,890 1 Thisinvention relates to a process of forming rigid'shapes of oriented resinpolymer and to a method of making such shapes. It has particular.

2 Claims. (or. 13-59) relation to relatively large shapes of relativelyhigh strength formed from certain resin polymers which producebrittleand hence relatively weak rigid shapes when molded by the usualinjection or' compression methods. The resin polymers molecularorientation, such whichpolystyrene is an'example.

Such resin polymers have certain valuable properties which make theiruse desirable and which are capable of as vinyl polymers, of

therefore if their inherent brittleness or weakness is overcome, the useof stantially increased. It is known that the tensile strength andtoughness of such polymers may be substantially inthe polymers can besubcreased by molecular orientation of thin sections such as fibers andfoils. Thus, polystyrene, though forming a brittle foil-or sheet whenformed bybrdinarymethods, may be toughened and made flexible bymolecular orientation. One method of. doing this is to extrude thepolymer in the form of asheet or ribbon and then to stretch it in bothtransverse and longitudinal directions at selected rates under selectedtemperature conditions to effect molecular orientation. The area ofthesheet is increased and its thickness reduced. The method of formingsuch sheet is not perse part of the present invention. Sheet or foilwhich is molecularly oriented by both transverse and longitudinalstretching is referred to herein as biaxially oriented. r

However, it is not feasible in most cases to strengthen or toughen rigidshapes or articles of unusual shape or size after they have been formedby any such method of molecular orientation because of the diiiiculty ofestablishing and controlling the necessary conditions and of stretchingsuch articles at the required rate and to the required degree.Therefore, such articles usually have had to be formed by heating mold-Furthermore, it is very diflicult and in some cases impossible to form"hollow shapes having relativelythin walls from resin polymers byinjection or compression methodsbecause of the high resistance of fiowoisuch polymers through narrow spaces. This is particnlarly true withregard to relatively large,thin' walled'articles having an end portion.connected to the sidewall of the articles. In addition, relativelyexpensive dies comprising both male and female portions, and costlymachinery, arerequired in producing such articles. bycompression' orinjection molding.

The general object "of this invention .is' to produce rigid, integralshapes, including hollow shapes, of highlybriente'd polymer and whicharticles therefore are relatively strong. Another object is to'produ'cefrigid integral hollow shapes of oriented resin polymer havinga side wall portion and anend portion connected to the side wallportion. i "j j A more specific object to produce rigid integral hollowshapes of orientedresin polymer for use as electrical insulation or thelike. Such articles may take the formj'of domes, covers or casingsforelectronic apparatus, supersonic apparatus; or for similar purposes. 7

'Still another object is toproduce relatively thin-walled rigid integralshapes of Oriented polymer. l

It alsois an object of the'invention to provide a novel processofflorming shapesof the character referredto abovefrom sheet or foils ofthe desired polymer, which sheet or fails have been molecularlyoriented. Thisis' accomplished by coalescing the sheet r foil-s byheatinto a solid, continuous or integral andn'on-lamellar mass 'of thedesired shape in 'whihqtheidentity of the sheet or foils is lostjornearly'lost, but under controlled conditions such that a substantialamount of the molecular orientationthereof is retained in the hollowshape. Preferably, the process is so performed that substantiallyall ofthe molecular orientation of the sheetor-foil' is retained in the finalarticles. r 1 1 a The present invention is particularly'distim guishedfrom prior processes and articles in that recover-y forces areestablished in the oriented sheet by h'eating the sheet-until elasticitydevelops and utilizing" these rower, preferably in" conjunction with lowpressure; to efi'ect the desired coalescence of thesheets-into theintegral non-lamellar 3 mass. These recovery forces are due to thetendency of the oriented sheet to resume or recover the shape anddimensions which it had before stretching and orientation, that is, thetendency to contract in the plane of the sheet and to increase inthickness. Substantial loss of orientation is prevented by restrainingthe contraction and thickening of the sheet and limiting the temperatureand. time of heating so as to prevent substantial relaxation ofmolecular orientation which can occur without contraction andthickening. Also the duration of recovery forces is limited by limitingthe time of heating so as to prevent rupture of the sheet.

From the foregoing, it will be apparent that the articles produced bythis invention contain? potentially high recovery forces whichim'akethemv However, the articles can be unstable to heat.

sections, two of which are shown at 22a. and 2217, Fig. 6, so that thethe cylindrical portion 22 of the mandrel or form can be collapsedinwardly. The. sections'of the cylindrical portion of the form ormandrel are, ingeneral, arranged to fit together and are held togetherfor shaping operations and in a manner and by means, the detailsofgwhichare not illustrated, because well knowninthe molding art. It issufilcient to explainthat after the molding operation the secused for agreat many purposes in whichthey I are not heated sufficiently toestablish or release the recovery forces.

other Meets and advantages ,o he-invention, will be pointed out in thefollowing specifi ti or will become apparent therefrom, or from theaccompanying drawings, which depict various embodiments of the inventionand in which drawmgs:

Figs. 1 to 6 inclusive show, successive steps in thejnovel method forproducing a rigid nonlamellar dome of oriented polymer from molecularoriented sheetof such polymer;

Fig. 7 isa View showing the dome formed by the steps of Figs. 1 to 6being removed froma form;

Figs. 8 and 9 are'enlarged detailed views showing a preferred Way ofarranging and connecting separate assembliesof sheetjfand the structurethereby obtained;

Figs. 10 and ll are-views of preformed curved segments oforientedresinpolymer, which may be employed't'O form the, end pbrtibhofthe dome as illustrated in Figs. '3 'fand 143' Figs. l2and113show.otherpreiormed-shapes of oriented polymer whichmay be employed-to formtheend of a dome; and. Y I

Fig. 14..sliow's ,a preformed sheet of oriented polymer fortheproduc'tion of.agdiffer ent form .of dome illustrated in Fig. 15,. I,

It will. be. understood that variations and changes may be niadeias'tothe. types or. shapes of articles prod'ced and". as to" the. manner inwhich the method 'is performed, without departing from the scope of'th'appended claims."

The invention will ,be described in itsapplicationto the production ofhollow shapes of polystyrene, anihherentIybrittIereSin polymer havingvaluable properties, such as alow. power factor, which makesitesp'ecially useful in electronics. Other'resinpolymers capable ofbeing molecularly oriented. maybe employed. The polystyrene is employedin the form of flexible sheet or foil which has been molecularlyoriented, preferably by stretching the. sheet transversely and'longitudinally. Thus, the sheet or foil may be orientedbyincreasing itsarea by a factor of I2" by transverse and longitudinal stretching underconditions; controlled-to provide sheet or foil having a high degree oforientation. However, in some cases onforsome portions of the article tobe ;produced ,the sheet may be relatively stiff rather than flexible andalso may be especially shaped r preformed to-a; desired shape or u v tuappr x mat nesthatp rt n o th article which is therebyttq,be. 9n tut d-,

s l ust ated in; Fi s; 1 te-1'1; the ho lowrtic e tions of the portion22 are moved inwardly, as showriinF-ig 7, to-free the article forremoval.

'IEhebottom;ends of the sections 22a-22b are chamfered at 2 Fig. '7, asalso is the upper edge of-the member 2-3- asindicated at 25, so thatthese partsymay fit together, as shown in Fig. 6, and may be separatedas shown in Fig. 'I by moving the sections inwar ly.

The sections. 22a, 22b of the portion .22: rest upon the member 23 andthe mandrel thus formed is supported or suspended by means-.0: acjentral shaft26; the lower end of which'is suitably secured in thecentral lug, 21 which.rises from theinterior of the member 23. e

The form 21 is provided with a cover 28', Figs. 5j a d 6; chamfered tofitthe upper edgesofthe sections 22 a-=-22b,as shown at 29, andprojecting outwardly to; provide a forming flange13l. The cover 28 isconnected to a. suitable source of vacuum, not shown, through a pipe 3 2and'the sections ,22aand22b and the mandrel portion 23 have numerousholes 33 therein for applyingfthe vacuum to the exterior ofthemanjdrelfor, the

purposes described below. Other members or 8.. v The assembly of layersthusprovided;- has an approximate shape and size ofthe. sidewall-portionof the dome to-be formed and when the windinghasbeen completed, theouterffree end may be-held in place temporarily bytapes, as

shown at 36,. Figs. 2, 3 and 4, to preventunwind- A-.fiange-may beformed on the dome by winde inga narrowstrip 31 of oriented resi'npolymer overthe winding 34 ;and against the underside .of "flange fluntil the thickness of the layers is sufficient to form-theflange to thedesired radial thickness; Theend of thisWinding also maybeheId-EinjpIace temporarily by; atape, as indicated at 38, Fig. 3. IHowever,- this tape may be removed and; v the winding of the ribbon 31held in place by means of a steel ring 39 whichhasa tightsliding-ntover'the outer edge oi-the-cover tapered bottom edgeportionat35, Figs. 1,5, and

28 and which in addition to holding winding 31 in place assistsinforming the flange; as ex plained below. 1

The formation of a flange on the dome may be assisted by'employing aribbon 31a,;Fig.5a, of greater width than the length of the flange to beformed and so located that the cover 28 will be supported by the winding37min spaced relation to form 22 as shown in Fig. a. Theapplication oivacuum and heat, as explained-below. will permit seating of cover 28 andthe formation of a solid flange even though the winding may initiallycontain as much as 30% air by volume in the flange forming space. a

To form the semispherical end of the dome, suitably preformed,molecularly oriented sheet is assembled in the desired number of layersover the end portion 23 of the form'or mandrel 2| and in overlappingrelation to the bottom edge portion of the cylindrical winding toprovide a semispherical assembly of layers as indicated generally at),

Fig. 3. These preformed members may have various shapes. Asillustratedin-Figs. 3, 4 and 5, theyare made of sections of asemisphere,there being'a number of sets or groups comprising three sections each.Two of these sections, shown at 4| of Figs. 3 and 4, have the formillustrated in Fig. 11. They may be placed on the member 23 with theirrespective pointed ends Ma touching and the third section 42 is thenplaced in position so that its edges overlap the inner edges of thesections 4|, as indicated at 42a and 421:, Fig.- 3. The form of thesection'42 is shown in Fig. from which it will be seen that it isprovided withztabs 42c and 42d by means of which the section 42 is drawntightly into position on the form but which may be cut off, as shown at42e,

in line with the upper edges of the sections 4| of the same group orset. i

The sets ofsections preferably are applied to the form successively instaggered relation so that the overlaps 42a and 4222 are angularlyspaced about the axis of the dome, as indicated by the cut ends 42c,Figs. 3 and 4, of the section 42 of the respective sets of sections.This avoids unduly and locally thickening the end of the dome by theoverlaps 42a and 42b. i i

The sections 4| and 42 may be held together temporarily by tapes" andthe sets of sections may be held in assembled relation with thecylindrical winding by tapes 44.

Instead of employing the sections 4| and 42 of Figs. 10 and 11, integralsemispherical-preforms of oriented polymer may be used, such as shown at45, Fig. 12.

The preformed elements, such as those of Figs. 10, 11 and 12, which arespherically curved may be formed by heating a sheet of the polymer andforming it to the desired shape by means of a male drawing die or byblowing it with or without the aid of a female die, or the heated sheetmay be shaped by drawing it into a female die by means of a vacuum. Suchdies are old in the art and hence are not shown in the drawings. Thesheet may be heated by airor by steam. Sheet which has been previouslymolecularly oriented may be employed and if such sheet is used the timeof heating is made very short or the sheet is heated to arelatively lowtemperature, to prevent as much as possible loss of orientation, whilepermitting the sheet to be softened sufliciently for the shapingoperation. Bya proper control of temperature, time of heating andrapidity of the forming operation, orientation of the sheet may beincreased to a degreehigher than that initially suitable clamps (notshown) in forming it by any of the above methods. v

The curved end of the dome also may be provided for by the use of anumber of preforms of the type shown at 46 in Fig. 13. Preform 46 isaircular and flat and is cut out, as indicated at 46a, i

to provide a number of centrally connected sections 46b of such shapeand size that the preform can be brought into approximatelysemispherical shape by overlapping the edges of these sections. in theuse of the elements 4| and 42 in Figs. 3 and 4, the preforms-45 may beso arranged that the overlaps thereof are staggered.

Referring again to Figs. 3, 4 and 5, it will be seen that thesemispherical assembly 40 is made "up of elements which are of outwardlydiminishing depth, or inwardly increasing depth. This is more clearlyshown in Fig. 8 from which it may be seen that an inwardly taperedupperedge portion is provided at 40a which overlapsthe tapered edgeportions 35 of winding 34. i

This method of forming and overlapping the assemblies 34 and 4|] ispreferred because itavoids internal edges which are objectionablebecause, unless a high external pressure is employed in the formingoperation or the edges are tapered, voids are formed between such--internal edges andthe material onopposite sides of such edges. Thus, itwill be seen from Fig. 8 that all the edges of tapered portion 40a areexternal to the outer surface of the assemblies andall of the edges ofthe tapered portion 35 areexternal to the inner surface of theassemblies. No edge is overlapped by two layers and hence no voids canbe formed where the connection is made between the two assemblies. Inaddition, the tapered portions form a wall of substantially uniformthick- The entire assembly of oriented polymer may now be covered by aflexible, liquid-proof bag 48 of rubber or other suitable material andthis may best be done by first rolling up the bag, applying it to thebottom end of the assembly and unrolling it up and over the assembly,the various tapes applied to hold the layers in place preferably beingremoved as the bag is unrolled. The bag preferably is of suificientlength to cover the ring 39 and to extend upwardly therefrom so that itmay be securely clamped on the cover 28 by means of aclamping ring 49,Figs. 5 and 6.,

A vacuum is applied to the assembly through.

connection 32 and perforations 33 whereby all: air is exhausted frombetween the layers of sheet and an outside pressure is created on thebag: 48 to hold the sheet in place and assist in the forming operation.The assembly is now ready for heating to form the hollow article.

Heating preferably is conducted by immersing the assembly in a suitableheating bath, such as shown at 5|, in a container 52 heated by a burner53. A suitable heat transfer liquid is ethylene glycol. I i

' lamellar mass.

The assembly is heated in the bath ata temperaturefor a period selected.toestablishme covery forces in the oriented sheet. Such heat ing softensthe sheet suficientlyto permit the recovery forces or stresses,;,augmentedby the external pres-sure on the bag'jii to cause the layersof sheet-to coalesce into an;integralnon- This probably occurs inaboutminutes after a uniform temperature has been I established and theinner layers have reachedthe temperature ofhigh elasticityatwhichrecovery forces or stresses are developed in the sheet. The temperatureand time of heating preferably are so selected and limited and therecovery forces so limited, held or restrainedlthat actual recovery isvery slight, rupture of the 'sheet and separation of overlapsareavoided,

and relaxation of molecular orientation does not occur or is notsubstantial. Although a temperature of heating isused which is highenough for relaxation to occur, the time of heating at such temperatureis insuflicientto permit substantial strength than can beformedbyprdinary mold.-

;.Wantagespi prior-methods are a-voided particularly in theproduction ofunusually'large shapestion temperature here referred to is determined bythe method disclosed in- Transition temperature and cubical expansion ofplastiematerials, by Fred E. Wiley, Industrial and-EngineeringChemistry, vol. 34, page 105 September 1942. The heating temperatureshould be substantial lyabove the transition temperatureto speedup theforming, operation. The heating may a be 1 performed with a heating 1bath maintained at 220-280 F.

For the production of a dorne such' as shown in Figs. 1 to 7, ofapproximately 25 inchesin diameter, approximately 31 inches longan dhawing a wall approximately .060. of aninchthicI;

and a flange thick from' bi-axiallyoriented (transversely andlongitdinally stretched} -.polystyrene-sheet of .005 to .010 inch thickthe as sembly may be held in the bath at 245? for 3" hours, or at 265 F;for 2 hours, with goodgresults Recovery of; the layersis restrained soas to prevent separation thereof where they overlap by the applicationof holding pressure. Thus the application oi vacuum to the interiorof-the form creates. a difierential pressure which-V is effective onthebag 48 and the exterior of the assembly. to restrain recovery ofthe'layerst-and-to assist in the forming operation. .In addition, the

internal vacuum assists in removing; air; from between'the'layerswhicnalso-is-squeezed out by;

the recoyeryiorces.

Also, holding and forming pressure is de veloped by ring 39 due to theslight thickening of thelayers of winding 37 as they'contractandcoalesce into a. solid mass whicn causesrecovery,

ciorces to build-up in the layers'between ring39 and the u perend offornrZ-i. In thisycasethe holding pressure is va pressure -of reaction."It will be apparent that the ring-3-9 v restrains re covery of thelayers between it and the form-2|."

8 It probable thatslight-softening of the layers takes place and causesthem to stick together before they can contract and separate as theresult of'the development of the recoveryiorces.

If. desired the top of chamber; 52 maybe closed and positive pressureapplied through the liquid bath tobag 4B and the; layers of the assembly.to

provide holding and forming pressure in lieu of V or f to augment thatresulting from --internal vacuum.

Various hollow shapes; other than cylindrical shapes with semisphericalends,-may; be made embodying and in accordance with'this invene *tion.Thus, a hollow shape of-.parabolio;lform,

sueh as shown in Fig..15, maybe made. vTo make "such a shape. a sheet54' of oriented polymer, Fig; 14, may be cut out as shown at 55 'toprovide taperedstrips '56 thereon This sheet may then be wound on asuitable form. and strips Fit-held thereon-in overlapping relationagainst thcform and against theinner layers of thesheet. The end of thearticle mayrboformed -of preshaped elementsil of oriented polymerassembled with the winding of sheet/ 54 as shown in Fig. 15. The'{entire assemblymay -then-be formed intofarigid "non-lamellar article of-orient;ed polymer. as a de,-.

scribed above.: I

From the foregoing it mer may be formed :of ssubstantiallygreater ingmethods thus overcoming the inherent brittleness of articles producedbysuch methods-H At thesarne time; high mold COSt5fa,l1dg )th l disadorhollow shapes.

Thearticles produced by-this inventioncan 7 be distinguished fromarticles-produced by other sce iodspby te s w h alzt hiehst n th or;toughness of these products and the arrangeentrsn v molecular rien at hch en a y corresponds in pattern and degree. to that of the assembledsheet or foil; frorn which the,;- art ic1es.

" r sma a en-( 9; st ce i hedimar-15s,- lines'or edgeswhich m-aysremainonfthe surface of the article; as \theresultor slight,unevencontractiom-of v the layers orv of-. pa rtial overlappingofthelayersieven though the struciture of thearticle-is non-lamellarHaving thus described ollrinvention; what we desire to claimalldfiECllI'flbYLettBlS Patentis: 1

1. The; process 'of :forming an integral hollow article of. orientedolymer having at wall -portion -"and a curved end portion whichcomprises -as-;

seinbling on a form; layers of orientedpolyrner for the' Wa'ILp rtionOfthe article, thencassemblingon theiorm curved *laye-rsof orientedpolymer for the end portion of V the article in overlapping relation tothe first-named layersgheatg th enti essembl until h ay rs. are-coasee it an inte ra -mass a ain nsih overy h a rs; du i uc he tin t p ev n rtionhoi h wa l :f rm s. l ers athema io mi elaye sv e e roq se ormin a tn es a hollow t-Med r en edr olrm r havins a ll portion nd el endt onich:.co r s r s embl ne on a fornr layers of biaxially oriented polymere; W 4 q fi nwo a t c e/ e 6 .11 1 bling on the form.- hollow layers;-of oriented poly-- mer for-.t-he end portiongof saidarticle in overi g:et nt th fir tmed:la rs: c

ing h sht ea semlqly with; a ex ble ewimu e ne th embl Q id mee in a hiwill; be seengthatirigid; integral, non lamellar articles of oriented,polyholding the assembly in the bath only long REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 460,086 Harvey Sept. 22, 18911,727,483 Mozzelt Sept. 10, 1929 Number Number Name Date Meurling June13, 1933 Carroll Oct. 17, 1933 Wheatley Sept. 10, 1935 Owen Sept. 22,1936 Schmidt Jan. 5, 1937 Studt et a1 Mar. 16, 1937 Bergstein Apr. 19,1938 Ushakoff Apr. 1, 1941 Austin Jan. 12, 1943 Reach Feb. 2, 1943Grundel Mar. 28, 1944 Sloan Nov. 14, 1944 Conner Mar. 2'7, 1945 FOREIGNPATENTS Country Date Great Britain Jan. 6, 1936

